Benthos — Illinois River 



In 1915, Richardson (1921a: 490-493) took a total of seventy-three 

 bottom samples between river miles 80.0 and 0.0. He used two types of 

 iron dredges, which were hauled for distances of two or five feet along 

 the bottom, and another device called a mud-dipper. He took care to de- 

 termine the amount of bottom material and the number of organisms taken 

 by each sampler in a series of parallel hauls, so that the results could 

 be expressed in quantitative terms, as the number of organisms taken per 

 unit of bottom area (Richardson, 1921a: 364). He also compared the ef- 

 ficiency of his sampling devices with a Petersen grab sampler, a device 

 still used today (for example, see Colbert et al., 1975: 23). 



In 1915, the study reach of the Illinois River had the lowest 

 density and diversity of benthic organisms of any of the reaches Richardson 

 studied (Richardson, 1921a: 404, 417). The biomass in this reach of 

 the river was less than one-twenty-fifth of the average in the lower 

 120 miles and less than one two-hundredth of the biomass in the vicinity 

 of Havana (Richardson, 1921a: 410-412). Richardson (1921a: 474-475) 

 gave the following reasons for the relative paucity of benthos in the 

 study reach: (1) The bottom was well scoured and there was a lack 

 of soft mud substrate due to higher current velocities, which in turn 

 were attributable to a greater rate of fall in the main channel and 

 confinement of the river between lateral levees. (2) The channel was 

 dredged more frequently. (3) The absence of backwater areas (as a 

 result of leveeing) concentrated the feeding activities of the annual 

 upstream runs of large carp and buffalo in the spring. 



On January 1, 1900, the Sanitary and Ship Canal was opened at 

 Chicago, connecting the DesPlaines and Illinois Rivers with Lake 

 Michigan. The canal was used to flush municipal and industrial wastes 

 into the Illinois River system and away from Chicago's municipal water 

 intake in Lake Michigan. 



The quantity and quality of water diverted through the canal had 

 a tremendous impact on the Illinois River. Water levels at Havana, 

 Illinois (river mile 120) rose an average of 2.8 feet and, during the 



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